Voltmeter and Ammeter

        Based on the schematic provided by JLCPCB's current and voltmeter training camp, this design incorporates some minor modifications:
       1. Some components, such as capacitors and resistors, have been replaced with surface-mount packages. While this doesn't optimize the wiring to reduce overall size, it reduces the surface area occupied by components, exposing more of the circuit board and allowing for the display of color silkscreen images.
       2. The component layout has been altered, with voltage measured on the left and current measured on the right. The digital display also shows the voltage value on the left and the current value on the right. Pin definitions are clearly indicated on the silkscreen.
       3. The power supply interface has been replaced with a Type-C interface, allowing for easier power supply via a mobile phone charger or USB cable. Both CC1 and CC2 interfaces utilize 5.1K pull-down resistors to ensure power supply via C-to-C cables. Two header pins are also provided for direct DC power supply, and the LDO chip used allows for a maximum input voltage of over 30 volts.
    4. The program uses the "current and voltmeter with calibration function" from the training camp. The hex file can be directly burned using the "cw programme" software. The compressed package contains the Keil project source code.
 The functions of the buttons are as follows:  
Define 5 working modes. The K1 button is used to switch the display mode. The K2 button sets the parameter value for the corresponding mode and saves it to FLASH. The K3 button returns to mode 0.
Mode 0: Displays normal voltage and current values ​​(the left digital tube displays the voltage value *.V or .*V automatically, and the right side displays the current value _.**A).
Mode 1: 5V voltage calibration value setting. The left digital tube displays 5.05. The right side displays the current voltage value _.V or ._V. In this mode, the multimeter should be set to 5.00V to measure the measured bit. After pressing the K2 button, the current value is calibrated to 5V.
Mode 2: 15V voltage calibration value setting. The left digital tube displays 5.15. The right side displays the current voltage value _.V or ._V. In this mode, the multimeter should be set to 15.0V to measure the measured value. After pressing the K2 key, the current value is calibrated to 15V.
Mode 3: Current 0.5A calibration setting. The left digital display shows A.0.5. The right display shows the current current value _.**A. After pressing the K2 key, the current value is calibrated to 0.5A.
Mode 4: Current 1.5A calibration setting. The left digital display shows A.1.5. The right display shows the current current value *.**A. After pressing the K2 key, the current value is calibrated to 1.5A.
    4. Physical demonstration: